Hi Silang. Far more concerning than a single French word in the Book of Mormon are the many, many English words. How did these ancient peoples know English! ? !

I say this joking, of course. The Book of Mormon is a translation. The original writers spoke neither English nor French. Joseph Smith likely chose to use the word adieu because it concisely conveyed a sense of finality.

I hope this answer helps. All the best.

Jim

April 19, 2017

Adieu! I loved that phrase when I saw it in the Book of Mormon. I thought the same thing